/**
* 抖码算法，让算法学习变的简单有趣
* @作者 : 老汤
*/


 // Definition for singly-linked list.
struct ListNode {
    int val;
     ListNode *next;
    ListNode() : val(0), next(nullptr) {}
    ListNode(int x) : val(x), next(nullptr) {}
    ListNode(int x, ListNode *next) : val(x), next(next) {}
};

class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        ListNode* dummyNode = new ListNode(-1);
        dummyNode->next = head;

        ListNode *slow = dummyNode;
        ListNode *fast = dummyNode;

        while (n-- >= 0) {
            fast = fast->next;
        }

        while (fast != nullptr) {
            slow = slow->next;
            fast = fast->next;
        }

        ListNode *delNode = slow->next;
        slow->next = delNode->next;
        delNode->next = nullptr;

        return dummyNode->next;
    }
};